The present invention relates to catalytic polymerization, in general, and, tactic catalytic polymerization, in particular, of alpha-olefin monomers using an active non-metallocene pre-catalyst featuring a diamine diphenolate complex, and a corresponding method using the disclosed pre-catalyst.
Currently, there is significant interest relating to methods and systems of catalytic polymerization of alpha-olefin monomers based on a xe2x80x98pre-catalystxe2x80x99 featuring a metal bound to one or more spectator ligands, where the pre-catalyst may be soluble in a liquid phase solvent, or is adsorbed on a solid surface, and where alpha-olefin monomer reactant may be liquid or gas phase. In such methods and systems, typically, the pre-catalyst is activated by at least one xe2x80x98co-catalystxe2x80x99, where the combination of the activated pre-catalyst and the at least one co-catalyst functions as a single chemical entity, or complex xe2x80x98catalystxe2x80x99, for polymerization of the alpha-olefin monomer. The field of catalytic polymerization of alpha-olefin monomers is of significant industrial importance, as more than 50 million tons of poly(alpha-olefin) products, such as polyetheylenes and polypropylenes, are produced each year, involving metal based catalytic processes and systems.
Hereinafter, the term xe2x80x98pre-catalystxe2x80x99 refers to a chemical entity, in general, and to a chemical compound, in particular, which, when activated by at least one xe2x80x98co-catalystxe2x80x99, becomes part of a xe2x80x98catalystxe2x80x99 functional for catalytic polymerization of an alpha-olefin monomer, under proper polymerization reaction conditions. In general, without the presence of at least one co-catalyst, a pre-catalyst is ineffective for catalytic polymerization of an alpha-olefin monomer, and consequently exhibits essentially no catalytic activity for polymerization of an alpha-olefin monomer. Here, when referring to catalytic activity during a polymerization reaction, reference is with respect to the catalytic activity of a pre-catalyst, and it is to be understood that the pre-catalyst functions in concert with at least one co-catalyst for effecting catalytic polymerization of an alpha-olefin monomer. It is noted, however, that there are rare exceptions of a particular pre-catalyst functioning without first being activated by a co-catalyst, for effecting catalytic polymerization of an alpha-olefin monomer. Thus, the present invention focuses on a new and novel pre-catalyst compared to pre-catalysts currently used for catalytic polymerization of alpha-olefin monomers.
Currently, one of the major goals in this field is to produce a variety of new types of poly(alpha-olefin) products, for example, tactic polymers made from alpha-olefin monomers featuring more than two carbon atoms, having well defined bulk or global physicochemical properties, such as mechanical strength, elasticity, melting point, and chemical resistance, applicable for manufacturing a diversity of end products. This may be achieved by controlling the polymer tacticity and polymerizing different types of alpha-olefin monomers, in order to produce a variety of homo-polymers and co-polymers, with varying degrees of monomer incorporation.
Bulk or global physicochemical properties of polymers are directly related to, and are controllable by, molecular or local physicochemical characteristics of the polymer units making up the bulk polymer. Three notable molecular physicochemical characteristics are polymer molecular weight, polymer molecular weight distribution, and polymer tacticity.
Polymer molecular weight and polymer molecular weight distribution are highly relevant with respect to producing different types of polymers. For example, ultra-high molecular weight polyethylene (UHMWPE), having an average molecular weight above 3,000,000, has the highest abrasion resistance of thermoplastics and a low coefficient of friction. Unlike synthesis of small molecules, however, polymerization reactions involve random events characterized by formation of polymer chains having a range of molecular weights, rather than a single molecular weight. Typically, polymers are better defined and characterized in relation to narrow molecular weight ranges.
The accepted parameter for defining polymer molecular weight distribution is the polydispersity index (PDI), which is the weight average molecular weight, Mw, divided by the number average molecular weight, Mn, or, Mw/Mn. Depending upon the actual application, ideally, a catalytic polymerization system features xe2x80x98livingxe2x80x99 polymerization in which the rate of initiation is higher than the rate of propagation leading to a PDI of close to 1, and involving a single catalytic active site, and the rate of termination reactions is negligible relative to propagation. This has been achieved in very few systems for catalytic polymerization of alpha-olefin monomers. A PDI of 2.0, signifying xe2x80x98non-livingxe2x80x99 polymerization, is often found in metallocene catalytic systems, also involving a single catalytic active site. Classical heterogeneous Ziegler-Natta catalytic systems usually lead to a broader range of molecular weights with a PDI of about 5. One current challenge is to design alpha-olefin polymerization pre-catalysts, and catalytic systems including such pre-catalysts, leading to poly(alpha-olefin) products with low values of PDI.
Another current challenge in the field of catalytic polymerization of alpha-olefins is to design alpha-olefin polymerization pre-catalysts, and catalytic systems including such pre-catalysts, leading to poly(alpha-olefin) products having controllable and classifiable degrees of polymer tacticity. Polymer tacticity is another very significant molecular physicochemical characteristic of a polymer which can dramatically determine and influence bulk physicochemical properties of a polymer, such as a poly(alpha-olefin) polymer. The term xe2x80x98polymer tacticityxe2x80x99 refers to the particular micro- or local structural configuration of the substituents on the polymer backbone, or equivalently, stereo-regularity of the polymer chain, as to whether a polymer is, for example, isotactic, syndiotactic, or, atactic. Polymer tacticity is typically used in reference to a hydrocarbon polymer derived from polymerization of a monomer having more than two carbon atoms, such that the polymer has a side chain on every other carbon atom of the polymer backbone. Moreover, there are different particular forms or types of xe2x80x98polymer tacticityxe2x80x99 according to the particular micro- or local structure in terms of the relative orientations of the side chains bound to the polymer backbone.
A polymer in which all the side chains extend or protrude from the same side or plane of the polymer backbone is referred to as an xe2x80x98isotactic polymerxe2x80x99 which is obtained from an xe2x80x98isotacticxe2x80x99, or equivalently, an xe2x80x98isospecificxe2x80x99 polymerization process. A polymer in which the side chains alternately extend or protrude from opposite sides of the polymer backbone is referred to as a xe2x80x98syndiotactic polymerxe2x80x99 which is obtained from a xe2x80x98syndiotacticxe2x80x99, or equivalently, a xe2x80x98syndiospecificxe2x80x99 polymerization process. A polymer in which the side chains randomly extend or protrude from either side of the polymer backbone is referred to as an xe2x80x98atactic polymerxe2x80x99, which is obtained from an xe2x80x98atacticxe2x80x99 polymerization process. Furthermore, extent or degree of a particular form or type of polymer tacticity is also used in reference to polymer tacticity. For example, a polymer may be classified as being eighty percent isotactic and twenty percent atactic. Another example is a hemi-isotactic polymer, in which every second side chain extends or protrudes from the same side or plane of the polymer backbone, whereas the rest of the side chains randomly extend or protrude from either side of the polymer backbone. Typically, extent or degree of tacticity of a polymer, or a polymerization process, is determined by subjecting the polymer, or products of the polymerization process, to NMR spectroscopic analysis, more particularly, 13C NMR.
An illustrative example showing the dramatic influence polymer tacticity has on bulk physicochemical properties of a polymer is tactic polymerization of propylene. Isotactic polypropylene is solid and semi-transparent at room temperature with a melting point in the range 150-165xc2x0 C., syndiotactic polypropylene is a transparent solid at room temperature with a melting point of about 145xc2x0 C., and atactic polypropylene is a viscous oil at room temperature.
Metallocene pre-catalysts, featuring a metal complex including a metal atom, for example from Group IV transition elements such as titanium, zirconium, and hafnium, bound to two ligands from the well known cyclopentadienyl (Cp) family of ligands such as pentamethylcyclopentadienyl, indenyl, or fluorenyl, were introduced during the last two decades for the purpose of catalytic polymerization of alpha-olefin monomers. The most common type of metallocene pre-catalyst is a neutral complex including a metal in oxidation state of +4, bound to two anionic ligands in addition to two standard Cp ligands, for example, bis(cyclopentadienyl)titanium dichloride, also known as titanocene dichloride. A particular group of metallocene pre-catalysts is known as ansa-metallocene complexes, in which the two Cp type ligands are covalently bonded to each other. A related group of complexes is xe2x80x98constrained geometryxe2x80x99 pre-catalysts, featuring a metal bound to both a single Cp type ligand and a second anionic group, where the Cp ligand and second anionic group are covalently bonded to each other.
Using metallocene and metallocene type pre-catalysts in catalytic processes and systems for polymerization of alpha-olefin monomers affords better control of molecular weight and narrower molecular weight distribution, associated with lower values of PDI, relative to the classical Ziegler-Natta family of pre-catalysts such as titanium trichloride using a trialkyl-aluminum co-catalyst. Moreover, the group of ansa-metallocene pre-catalysts is useful for producing polymers with controllable and classifiable degrees of polymer tacticity. Metallocene and metallocene type pre-catalysts, processes, and systems are well known and taught about in the art. These pre-catalysts, processes and systems are, however, limited in many respects relating to the above discussion.
Foremost, with respect to catalytic activity, metallocene type pre-catalysts typically exhibit relatively moderate activity for polymerizing a small variety of alpha-olefin monomers. With respect to poly(alpha-olefin) product types and variety, alpha-olefin monomers polymerized by metallocene pre-catalysts are mostly short chain ethylene and propylene, which are already well taught about. Metallocene pre-catalysts are limited in terms of availability and versatility. Metallocene type pre-catalysts are relatively difficult to synthesize, a fact which limits the possibility of developing new varieties of metallocene type alpha-olefin polymerization pre-catalysts.
Due to continued searching for new poly(alpha-olefin) products exhibiting selected well defined bulk physicochemical properties and molecular physicochemical characteristics, combined with the above limitations associated with metallocene pre-catalysts, there is growing interest in developing non-metallocene alpha-olefin polymerization pre-catalysts, and related catalytic processes, and systems. The main emphasis is on obtaining new alpha-olefin polymerization pre-catalysts which are readily available, exhibit relatively high stability, and can be used for improving control over industrially important polymer parameters such as molecular weight, molecular weight distribution, product types and variety, and, controllable and classifiable polymer tacticity.
The principle of controlling polymer tacticity by ligands design was first demonstrated for various catalytic systems featuring the group of ansa-metallocene complex pre-catalysts, as reviewed by Brintzinger, H. H. et. al. in Angew. Chem., Int. Ed. Engl. 34, 1143, 1995. Catalytic systems described therein usually lead to a PDI not less than 2.0, and suffer from the above described disadvantages and limitations of metallocene systems.
An example of a xe2x80x98half sandwichxe2x80x99 pre-catalyst, featuring a complex including one Cp type ligand and a heteroatom donor, is described by Sita, L. R., in J. Am. Chem. Soc. 122, 958, 2000. This half metallocene catalytic system is active with regard to polymer isospecificity and living polymerization of alpha olefin monomers. However, this system involves operating at commercially undesirable reaction conditions, such as at xe2x88x9210 degrees Celsius.
A non-metallocene alpha-olefin polymerization catalytic system is disclosed in U.S. Pat. No. 5,852,146, and features a bis(hydroxy aromatic nitrogen ligand) transition metal pre-catalyst, functioning with an activating methylaluminoxane (MAO) co-catalyst. Relatively high catalytic activity of about 4,000 grams/(mmole-pre-cat. hr) is reported for polymerization of ethylene only. Moreover, MAO is needed in large quantities as co-catalyst, which, in general, poses notable limitations relating to cost and containment. MAO used in large quantities is costly, and needs to be properly disposed of with regard to environmental considerations.
Living polymerization of 1-hexene is described by Schrock, R. R., in J. Am. Chem. Soc. 119, 3830, 1997, and is disclosed in U.S. Pat. No. 5,889,128. One of the non-metallocene pre-catalyst compositions described therein comprises a dimethyl complex in which the metal atom is chelated to a tridentate spectator ligand, which is activated by a non-MAO boron salt co-catalyst. However, only atactic polymeric products are obtained from this system.
Living polymerization of 1-hexene is also described by McConville, D. H., in J. Am. Chem. Soc. 118, 10008, 1996. They describe an active non-metallocene polymerization pre-catalyst, involving activation of a pre-catalyst featuring a dimethyl metal complex of a bis(amide) ligand, with a non-MAO boron Lewis acid as co-catalyst under room temperature, for producing atactic polymers.
Another active non-metallocene living 1-hexene polymerization pre-catalyst functioning with a non-MAO co-catalyst, is reported by Kim, K., in Organometallics 17, 3161, 1998. Similar to other teachings, the described catalytic system yields only atactic polymers.
A non-metallocene diphenolate pre-catalyst is reported by Schaverien, C. J., in J. Am. Chem. Soc. 117, 3008, 1995. Use of the disclosed pre-catalyst leads to highly isotactic poly(1-hexene), however, the polymerization process is not living.
Recently, the present inventors, in U.S. patent application Ser. No. 09/394,280, filed Sep. 20, 1999, disclosed of an ultra-high activity non-metallocene pre-catalyst featuring an amine diphenolate complex and a corresponding method for catalytic polymerization of alpha-olefin monomers using this pre-catalyst. However, only atactic polymers are obtained using the disclosed pre-catalyst at the indicated polymerization conditions.
In view of the above discussed limitations for polymerization of alpha-olefins, to one of ordinary skill in the art, there is thus a need for, and it would be highly advantageous to have an active non-metallocene pre-catalyst and corresponding method for catalytic polymerization of alpha-olefin monomers, not limited to activation by large quantities of a co-catalyst such as MAO, and also characterized by high stability, readily obtained or synthesized, and capable of producing different types and varieties of poly(alpha-olefin) products having high molecular weight and low molecular weight distribution, and, controllable and classifiable degrees of polymer tacticity. Moreover, there is a need of such a pre-catalyst and methods for producing alpha-olefin polymers other than polyethylenes and polypropylenes, having industrially applicable properties and characteristics.
The present invention relates to catalytic polymerization, in general, and, tactic catalytic polymerization, in particular, of alpha-olefin monomers using an active non-metallocene pre-catalyst featuring a diamine diphenolate complex. Moreover, the present invention features a general method for catalytic polymerization, including a particular method for tactic catalytic polymerization, of alpha-olefin monomers, using the disclosed diamine diphenolate pre-catalyst.
It is therefore an object of the present invention to provide general structures and general formulas of an active non-metallocene pre-catalyst for catalytic polymerization, in general, and tactic catalytic polymerization, in particular, of alpha-olefin monomers.
It is a further object of the present invention to provide general structures and general formulas of an active non-metallocene pre-catalyst for catalytic polymerization, in general, and tactic catalytic polymerization, in particular, of alpha-olefin monomers, wherein the pre-catalyst is a diamine diphenolate complex featuring variability of the metal atom, ligands, aromatic groups, aromatic group substituents, a bridging group, and bridging group substituents.
It is another object of the present invention to provide a method for catalytic polymerization, in general, and tactic catalytic polymerization, in particular, of alpha-olefin monomers featuring the use of an active diamine diphenolate pre-catalyst, wherein the pre-catalyst features variability of the metal atom, ligands, aromatic groups, aromatic group substituents, a bridging group, and bridging group substituents.
It is another object of the present invention to provide a method for catalytic polymerization, including tactic catalytic polymerization, of alpha-olefin monomers featuring the use of an active diamine diphenolate complex, whereby the polymerization process is essentially a living system.
Thus, according to the present invention, there is provided a compound having a general structure selected from the group consisting of structure 1 and structure 2: 
wherein each structure 1 and structure 2: each single solid line represents a covalent bond; each double solid line represents a bond having varying degrees of covalency; each dashed line represents a bond having a varying degree of covalency and a varying degree of coordination; the M is a metal atom covalently bonded to each O oxygen atom, and bonded with varying degrees of covalency and coordination to each N nitrogen atom; the X1 and the X2 are each a univalent anionic ligand covalently bonded to the metal atom; the X3 is a single anionic ligand covalently bonded to the metal atom; the R1 and the R2 are each a univalent radical covalently bonded to a different one of the N nitrogen atoms; the R3 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR3xe2x80x94 of the (C6)1xe2x80x94CHR3xe2x80x94Nxe2x80x94 bridging unit; the R4 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR4xe2x80x94 of the xe2x80x94Nxe2x80x94CHR4xe2x80x94(C6)2 bridging unit; each of the R5 through R8 is a univalent radical covalently bonded to a different one of the C carbon atoms of the (C6)1 first aromatic group; each of the R9 through R12 is a univalent radical covalently bonded to a different one of the C carbon atoms of the (C6)2 second aromatic group; and the Y is a divalent radical covalently bonded to and bridging between both of the N nitrogen atoms.
According to another aspect of the present invention, there is provided a compound of a general formula selected from the group consisting of: [{OR5R6R7R8(C6)1(CHR3)NR1YNR2(CHR4)(C6)2R9R10R11R12O}MX1X2] and [{OR5R6R7R8(C6)1(CHR3)NR1YNR2(CHR4)(C6)2R9R10R11R12O}MX3], wherein each general formula: the M is a metal atom covalently bonded to each O oxygen atom, and bonded with varying degrees of covalency and coordination to each N nitrogen atom; the X1 and X2 are each a univalent anionic ligand covalently bonded to the metal atom; the X3 is a single anionic ligand covalently bonded to the metal atom; the R1 and R2 are each a univalent radical covalently bonded to a different one of the N nitrogen atoms; the R3 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR3xe2x80x94 of the (C6)1xe2x80x94CHR3xe2x80x94Nxe2x80x94 bridging unit; the R4 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR4xe2x80x94 of the xe2x80x94Nxe2x80x94CHR4xe2x80x94(C6)2 bridging unit; each of the R5 through R8 is a univalent radical covalently bonded to a different one of said C carbon atoms of said (C6)1 first aromatic group; each of the R9 through R12 is a univalent radical covalently bonded to a different one of the C carbon atoms of the (C6)2 second aromatic group; and the Y is a divalent radical covalently bonded to and bridging between both of the N nitrogen atoms.
According to another aspect of the present invention, there is provided a method for catalytic polymerization of an alpha-olefin monomer, the method comprising the steps: (a) providing a diamine diphenolate pre-catalyst having a general structure selected from the group consisting of: 
wherein each structure 1 and structure 2: each single solid line represents a covalent bond; each double solid line represents a bond having varying degrees of covalency; each dashed line represents a bond having a varying degree of covalency and a varying degree of coordination; the M is a metal atom covalently bonded to each O oxygen atom, and bonded with varying degrees of covalency and coordination to each N nitrogen atom; the X1 and the X2 are each a univalent anionic ligand covalently bonded to the metal atom; the X3 is a single anionic ligand covalently bonded to the metal atom; the R1 and the R2 are each a univalent radical covalently bonded to a different one of the N nitrogen atoms; the R3 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR3xe2x80x94 of the (C6)1xe2x80x94CHR3xe2x80x94Nxe2x80x94 bridging unit; the R4 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR4xe2x80x94 of the xe2x80x94Nxe2x80x94CHR4xe2x80x94(C6)2 bridging unit; each of the R5 through R8 is a univalent radical covalently bonded to a different one of the C carbon atoms of the (C6)1 first aromatic group; each of the R9 through R12 is a univalent radical covalently bonded to a different one of the C carbon atoms of the (C6)2 second aromatic group; and the Y is a divalent radical covalently bonded to and bridging between both of the N nitrogen atoms; (b) preparing a first chemical entity featuring a particular form of the pre-catalyst of Step (a); (c) providing a co-catalyst suitable for activating the pre-catalyst of Step (a); (d) preparing a second chemical entity featuring the co-catalyst of Step (c); (e) forming a catalytic polymerization reaction system for the catalytic polymerization of the alpha-olefin monomer by mixing the first chemical entity featuring the pre-catalyst with the second chemical entity featuring the co-catalyst with the alpha-olefin monomer to be polymerized, whereby the co-catalyst activates the pre-catalyst for becoming a catalyst effecting the catalytic polymerization of the alpha-olefin monomer for producing at least one type of poly(alpha-olefin) product; (f) terminating the catalytic polymerization of the alpha-olefin monomer; and (g) isolating the at least one type of the poly(alpha-olefin) product.
According to another aspect of the present invention, there is provided a method for catalytic polymerization of an alpha-olefin monomer, the method comprising the steps: (a) providing a diamine diphenolate catalyst having a general structure selected from the group consisting of: 
wherein each structure 1 and structure 2: each single solid line represents a covalent bond; each double solid line represents a bond having varying degrees of covalency; each dashed line represents a bond having a varying degree of covalency and a varying degree of coordination; the M is a metal atom covalently bonded to each O oxygen atom, and bonded with varying degrees of covalency and coordination to each N nitrogen atom; the X1 and the X2 are each a univalent anionic ligand covalently bonded to the metal atom; the X3 is a single anionic ligand covalently bonded to the metal atom; the R1 and the R2 are each a univalent radical covalently bonded to a different one of the N nitrogen atoms; the R3 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR3xe2x80x94 of the (C6)1xe2x80x94CHR3xe2x80x94Nxe2x80x94 bridging unit; the R4 is a univalent radical covalently bonded to the C carbon atom of the xe2x80x94CHR4xe2x80x94 of the xe2x80x94Nxe2x80x94CHR4xe2x80x94(C6)2 bridging unit; each of the R5 through R8 is a univalent radical covalently bonded to a different one of the C carbon atoms of the (C6)1 first aromatic group; each of the R9 through R12 is a univalent radical covalently bonded to a different one of the C carbon atoms of the (C6)2 second aromatic group; and the Y is a divalent radical covalently bonded to and bridging between both of the N nitrogen atoms; (b) preparing a first chemical entity featuring a particular form of the catalyst of Step (a); (c) forming a catalytic polymerization reaction system for the catalytic polymerization of the alpha-olefin monomer by mixing the first chemical entity featuring the catalyst with the alpha-olefin monomer to be polymerized, whereby the catalyst effects the catalytic polymerization of the alpha-olefin monomer for producing at least one type of poly(alpha-olefin) product; (d) terminating the catalytic polymerization of the alpha-olefin monomer; and (e) isolating the at least one type of the poly(alpha-olefin) product.
According to another aspect of the present invention, there is provided a method for isotactic and living catalytic polymerization of 1-hexene monomer for forming isotactic poly(1-hexene) product, the method comprising the steps: (a) providing diamine diphenolate pre-catalyst [{N,Nxe2x80x2-bis(3,5-di-tert-butyl-2hydroxophenylmethyl)-N,Nxe2x80x2-dimethylethylenediamine}zirconium dibenzyl]; (b) preparing a first chemical entity featuring the diamine diphenolate pre-catalyst of Step (a); (c) providing boron Lewis acid co-catalyst [B(C6F5)3] suitable for activating the pre-catalyst of Step (a); (d) preparing a second chemical entity featuring the boron Lewis acid co-catalyst of Step (c); (e) forming an isotactic and living catalytic polymerization reaction system for the isotactic and living catalytic polymerization of the 1-hexene monomer by mixing the first chemical entity featuring the pre-catalyst with the second chemical entity featuring the co-catalyst with the 1-hexene monomer to be polymerized, whereby the co-catalyst activates the pre-catalyst for becoming a catalyst effecting the isotactic and living catalytic polymerization of the 1-hexene monomer for producing the isotactic poly(1-hexene) product; (f) terminating the catalytic polymerization of the 1-hexene monomer; and (g) isolating the isotactic poly(1-hexene) product.
The present invention introduces several benefits to the field of catalytic polymerization of alpha-olefin monomers, which, until now have been unattainable. For example, particular forms of the diamine diphenolate pre-catalyst of the present invention, when activated by a co-catalyst under mild reaction conditions, enable achieving isotactic (isospecific) polymerization of a variety of alpha-olefin monomers, such as polymerization of long chain alpha-olefin monomers, for example, 1-hexene or 1-octene, for forming a variety of poly(alpha-olefin) products such as poly(1-hexene) or poly(1-octene), having high molecular weight and low molecular weight distribution. Moreover, such catalytic systems can additionally be characterized as living. Furthermore, such isotactic and living catalytic polymerization systems can be implemented at practical commercial reaction conditions, including, in particular, operating at room temperature.
The diamine diphenolate pre-catalyst of the present invention is relatively stable under commercially applicable conditions for polymerization of alpha-olefin monomers. Moreover, the pre-catalyst, and related forms of the pre-catalyst, of the present invention are relatively simple to synthesize, primarily due to simple syntheses of the corresponding diamine di(2-hydroxyarylmethyl) ligand precursors, from a variety of commercially available inexpensive starting materials, compared to syntheses of metallocene type pre-catalysts.